1. Field of the Invention
This invention relates to a video data processing apparatus and method for combining video signals.
2. Description of the Prior Art A video data processing apparatus for transforming a video signal is known in the prior art, for example, from U.S. Pat. Nos. 4,791,581 and 4,965,844. In such a video data processing apparatus, a three-dimensional video image having a three-dimensional effect has been produced by adding a Z-axis to the two-dimensional effect of the X-axis and Y-axis on the screen. It is also known that a new three-dimensional video image can be produced by synthesizing or combining at least two three-dimensional video images. As an example, first and second video data produced from two digital video effect (DVE) systems can be combined by a third DVE system to form new video data.
FIG. 1 is a block diagram of a known DVE system. The DVE system comprises a mixing circuit 1 and a key signal generation circuit 2. The mixing circuit 1 is supplied with first and second video data S1 and S2, respectively, which are to be synthesized. The key signal generation circuit 2 is supplied with first and second depth data S1Z and S2Z which correspond to the first and second video data S1 and S2, respectively. The key signal generation circuit 2 decides the positional relation between the superimposed images, or the so-called priority, from the supplied first and second depth data S1Z and S2Z, and produces key data or a key signal SK which is supplied to the mixing circuit 1. The mixing circuit 1 determines which video data is to be selected from among the first and second video data S1 and S2 on the basis of the key data SK so as to produce composite video data S3. That is, if the value of the key data SK is 1, the first video data S1 is outputted as the video data S3. If, on the other hand, the value of the key data SK is 0, the second video data S2 is outputted as the video data S3.
FIG. 2 shows an example of a new or composite three-dimensional video image corresponding to synthesized video data produced by the above-described synthesizing technique. This new three-dimensional video image is formed from a first three-dimensional video image 6 corresponding to the first video data S1 and a second three-dimensional video image 7 corresponding to the second video data S2.
In this known system, however, the key data SK may cause an incorrect and undesirable video image to be formed. For example, consider the situation in which the key data SK indicates the positional relation of a part 9 of the video image which is located at an intersection 8 on a one-dot chain line 11 as shown in FIG. 2. In this situation, the key data may be formed by pixel units which may be conceptually indicated by bits of 0 or 1 as shown in FIG. 3. With such key data, notches may be produced at the intersection 8 between the first and second video images 6 and 7, respectively, as shown in FIG. 2.